Acrylic fibers and films which particularly are suited for thermal stabilization

ABSTRACT

AN IMPROVED PROCESS IS PROVIDED FOR THE PRODUCTION OF STABILIZED ACRYLIC FIBERS AND FILMS. A MINOR QUANTITY OF AN ALKALI METAL SALT OF AN ORGANIC SULFONATE IS PROVIDED IN INTIMATE ASSOCIATION WITH AN ACRYLIC FIBROUS MATERIAL OR FILM AND IS INCORPORATED THEREIN IN A NON-POLYMERIZED FORM. UPON HEATING (PREFERABLY WHILE PRESENT IN AN OXYGEN-CONTAINING ATMOSPHERE) THE THERMAL STABILIZATION REACTION IS PROMOTED BY THE PRESENCE OF THE ALKALI METAL SALT OF AN ORGANIC SULFONATE. THE RESULTING STABILIZED FIBROUS MATERIAL OF FILM IS FLEXIBLE AND NON-BURNING, AND MAY BE UTILIZED A FIRE RESISTANT FIBER, FABRIC OR FILM, OR OPTIONALLY CARBONIZED OF CARBONIZED AND GRAPHITIZED TO FORM A CARBONACEOUS FIBROUS MATERIAL OR FILM.

nited States Patent Oflice 3,779,983 Patented Dec. 18, 1973 3,779,983ACRYLIC FIBERS AND FILMS WHICH PARTICU- LARLY ARE SUITED FOR THERMALSTABILI- ZATION Andrew Di Edwardo, Parsippany, Robert Dix, Wayne, andJohn Riggs, Berkeley Heights, N..I., assignors to Celanese Corporation,New York, N.Y. No Drawing. Filed June 1, 1972, Ser. No. 258,788 Int. Cl.C08f 27/06 U.S. Cl. 26045.7 S 12 Claims ABSTRACT OF THE DISCLOSURE Animproved process is provided for the production of stabilized acrylicfibers and films. A minor quantity of an alkali metal salt of an organicsulfonate is provided in intimate association with an acrylic fibrousmaterial or film and is incorporated therein in a non-polymerized form.Upon heating (preferably while present in an oxygen-containingatmosphere) the thermal stabilization reaction is promoted by thepresence of the alkali metal salt of an organic sulfonate. The resultingstabilized fibrous material or film is flexible and non-burning, and maybe utilized as a fire resistant fiber, fabric or film, or optionallycarbonized or carbonized and graphitized to form a carbonaceous fibrousmaterial or film.

BACKGROUND OF THE INVENTION In the past procedures have beenxproposedfor the conversion of fibers formed from acrylic polymers to a modifiedform possessing enhanced thermal stability. Such modification hasgenerally been accomplished by heating a fibrous material in anoxygen-containing atmosphere at a moderate temperature for an extendedperiod of time.

U.S. Pat. Nos. 2,913,802 to Barnett and 3,285,696 to Tsunoda discloseprocesses for the conversion of fibers of acrylonitrile homopolymers orcopolymers to a heat resistant form. The stabilization of shapedarticles of acrylonitrile homopolymers and copolymers in anoxygen-containing atmosphere commonly involves (l) a chain scission andoxidative cross-linking reaction of adjoining molecules as well as (2) acyclization reaction of pendant nitrile groups. It is generallyrecognized that the rate at which the stabilization reaction takes placeincreases with the temperature of the oxygen-containing atmosphere.However, in the past the stabilization reaction must by necessity atleast initially be conducted at relatively low temperatures (i.e. belowabout 300 since the cyclization reaction is known to be exothermic innature and must be controlled if the original configuration of 'thematerial undergoing stabilization is to be preserved.

Accordingly the stabilization reaction has tended to be time consuming,and economically demanding because of low productivity necessitated bythe excessive time requirements. Prior processes proposed to shorten theperiod required by the stabilization reaction include that disclosed inU.S. Pat. No. 3,416,874. See also the processes of commonly assignedU.S. Pat. Nos. 3,592,595; 3,656,882; and 3,656,883; and the processes ofcommonly assigned U.S. Ser. Nos. 777,902, filed Nov. 21, 1968 (now U.S.Pat. No. 3,647,770); 109,669 and 109,672 (now U.S. Pat. No. 3,708,326),filed Jan. 25, 1971; and 200,- 183 and 200,184, filed Nov. 18, 1971.

While stabilized acrylic fibrous materials may be used directly inapplications where a non-burning fiber is required, demands for the samehave been increasingly presented by the manufacturers'of carbonizedfibrous materials. carbonized fibrous materials are commonly formed byheating a stabilized acrylic fibrous material in an inert atmosphere,such as nitrogen or argon, at a more highly elevated temperature. Duringthe carbonization reaction elements such as nitrogen, oxygen, andhydrogen are substantially expelled. Accordingly, the term carbonized asused in the art commonly designates a material consisting of at leastabout percent carbon by weight, and generally at least about percentcarbon by weight. Depending upon the conditions under which a carbonizedfibrous material is processed, it may or may not contain graphiticcarbon as determined by the characteristic X-ray diffraction pattern ofgraphite. See, for instance, commonly assigned U.S. Ser. No. 777,- 275,filed Nov. 20, 1968, of Charles M. Clarke (now abandoned) for apreferred procedure for forming continuous lengths of carbonized andgraphitized fibrous materials from a stabilized acrylic fibrousmaterial.

It is an object of the invention to provide an improved process forforming thermally stabilized shaped acrylic articles.

It is an object of the invention to provide an improved process forforming dimensionally stable flexible flameproofed fibrous materials andfilms derived from an acrylic polymer.

It is an object of the invention to provide a process wherein thethermal stabilization of an acrylic fibrous material or film isaccelerated.

It is another object of the invention to provide an improved process forforming stabilized fibrous materials and films derived from acrylicpolymers which results in a product which is suitable for carbonization,or carbonization and graphitization.

It is a further object of the invention to provide a process forconverting an acrylic fibrous material or film to a stabilized formpossessing substantially the identical configuration as the startingmaterial.

These and other objects, as well as the scope, nature and utilization ofthe invention will be apparent from the following detailed descriptionand appended claims.

SUMMARY OF THE INVENTION It has been found that in the stabilization ofan acrylic fibrous material or film selected from the group consistingof an acrylonitrile homopolymer and acrylonitrile copolymers containingat least about 85 mol percent of acrylonitrile units and up to about 15mol percent of one or more monovinyl units copolymerized therewiththrough thermal treatment, that an improved process results by:

(a) Providing the acrylic fibrous material or film in intimateassociation with about 0.2 to 10 percent by weight of an alkali metalsalt of an organic sulfonate, with the alkali metal salt of an organicsulfonate being incorporated therein in a nonpolymerized form and beingcapable of promoting the thermal stabilization thereof,

and

(b) Heating the acrylic fibrous material or film at a temperature ofabout 240 to 310 C. until a stabilized fibrous material or film isformed which retains its original configuration substantially intact andwhich is non-burning when subjected to an ordinary match flame.

The acrylic fibrous material or film utilized in the improved process ofthe present invention consists essentially of (1) an acrylic polymerselected from the group consisting of an acrylonitrile homopolymer andacrylonitrile copolymers containing at least about 85 mol percent ofacrylonitrile units and up to about 15 mol percent of one or moremonovinyl units copolymerized therewith, and (2) about 0.2 to 10 percentby weight of an alkali metal salt of an organic sulfonate with thealkali metal salt of an organic sulfonate being incorporated therein ina non-polymerized form and being capable of promoting the thermalstabilization thereof upon heating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Stabilized acrylic fibers andfilms may be conveniently formed in accordance with the process of thepresent invention by:

(a) Providing a solution of (1) an acrylic polymer selected from thegroup consisting of an acrylonitrile homopolymer and acrylonitrilecopolymers containing at least about 85 mol percent of acrylonitrileunits and up to about 15 mol percent of one or more monovinyl unitscopolymerized therewith, (2) a minor quantity of a stabilizationpromoting agent comprising an alkali metal salt of an organic sulfonate,and (3) a solvent for the acrylic polymer and the alkali metal salt ofan organic sulfonate, with the alkali metal salt of an organic sulfonatebeing dissolved in said solvent in a non-polymerized form,

(b) Forming from the solution an acrylic fibrous material or film havingincorporated therein a minor quantity of the alkali metal salt of anorganic sulfonate in a nonpolymerized form, and

(c) Heating the acrylic fibrous material or film at a temperature ofabout 240 to 310 C. until a stabilized fibrous material or film isformed which retains its original configuration substantially intact andwhich is non-buming when subjected to an ordinary match flame.

The acrylic polymer utilized as the starting material is formedprimarily of recurring acrylonitrile units. For instance, the acrylicpolymer should generally contain not less than about 85 mol percent ofacrylonitrile units and not more than about 15 mol percent of unitsderived from a monovinyl compound which is copolymerizable withacrylonitrile such as styrene, methyl acrylate, methyl methacrylate,vinyl acetate, vinyl chloride, vinylidene chloride, vinyl pyridine, andthe like, or a plurality of such monomers. The pendent nitrile groupspresent within the acrylic precursor are substantially uncyclized.

The preferred acrylic precursor is an acrylonitrile homopolymer.Preferred acrylonitrile copolymers contain at least about 95 mol percentof acrylonitrile units and up to about 5 mol percent of one or moremonovinyl units copolymerized therewith.

The stabilization promoting agent which is incorporated Within theacrylic fibrous material or film prior to the heating of the same is analkali metal salt of an organic sulfonate. The cation of the salt may beany of the alkali metals, and is preferably sodium or potassium. Thealkali metal salt of an organic sulfonate accordingly contains one ormore AO OX groups attached to an organic molecule where X is an alkalimetal. The alkali metal salt of an organic sulfonate is provided withinthe acrylic fibrous material or film in a free, nonpolymerized form andis chemically uncombined with the acrylic polymer. 'For instance, if thealkali metal salt of the organic sulfonate contains a polymerizablevinyl group within its molecule it is non-polymerized.

The chemical structure of the alkali metal salt of an organic sulfonateis not critical and may be varied widely so long as it possesses therequisite SO OX functional group. For instance, common anionicdetergents of a sulfonate type may be selected for use in the process.These compounds are commonly alkali metal salts of an alkylarylsulfonate (e.g. an alkylbenzene sulfonate). One or more straight orbranched chain alkyl group (e.g. having up to about 30 carbon atoms andpreferably to carbon atoms) may serve as a side chain positioned upon anaryl nucleus of the organic sulfonate. The readily available andrelatively inexpensive alkali metal salts of alkylaryl sulfonates arepreferably selected. Representative alkali metal salts of alkylarylsulfonates include:

sodium dodecylbenzene sulfonate, sodium toluene sulfonate,

sodium isopropyl naphthalene sulfonate, sodium isobutyl naphthalenesulfonate, sodium mesitylene sulfonate,

sodium monobutyl diphenyl monosulfonate, sodium ethyl benzene sulfonate.

Other representative alkali metal salts of organic sulfonates which maybe employed include:

sodium methallyl sulfonate,

sodium lauryl sulfonate,

sodium benzene disulfonate,

sodium betanaphthalene sulfonate,

sodium polypropylene sulfonate,

sodium alkenyl-l-sulfonate (see US. Patent 3,444,191), sodiumtetrahydronaphthalene sulfonate.

Sodium methallyl sulfonate is an example of stabilization promotingagents which possesses a polymerizable vinyl group. In the presentprocess such vinyl is nonpolymerized and forms no part of the mainpolymer chain within the acrylic polymer. For instance, the sodiummethallyl sulfonate or other polymerizable sulfonate salt is broughtinto intimate association with the acrylic polymer following thepolymerization of the same and in the absence of polymerizationcatalysts, etc.

The particularly preferred alkali metal salts of organic sulfonates foruse in the present process are sodium dodecylben-zene sulfonate, sodiummethallyl sulfonate, sodium benzene disulfonate, sodium laurylsulfonate, etc.

Suitable solvents for use in the present process are capable ofdissolving both the acrylic polymer and the alkali metal salt of anorganic sulfonate. Representative organic solvents includeN,N-dimethylformamide, N,N- dimethylacetamide, dimethyl sulfoxide,butyrolactone, and N-methyl-Z-pyrrolidinone. The preferred solvents arethose which are commonly utilized during the spinning of fibers fromacrylonitrile homopolymers and copolymers. The particularly preferredsolvents are N,N-dimethylformamide and N,N-dimethylacetamide.

The concentration of the acrylic polymer in the solvent may be variedwidely, e.g. about 5 to about 30 percent by weight based upon the weightof the solvent. Preferred concentrations range from 10 to 25 percentacrylic polymer by weight based upon the weight of the solvent.

The alkali metal salt of an organic sulfonate is present in the solutionof acrylic polymer in a minor quantity, i.e. about 1 to 20 percent byweight based upon the weight of the acrylic polymer. The concentrationemployed will vary with the fiber or film forming technique selected asdescribed hereafter. In a preferred embodiment of the process the alkalimetal salt of an organic sulfonate is present in a concentration ofabout 1 to 10 percent by weight based upon the weight of the acrylicpolymer.

In a preferred embodiment of the process wherein N,N- dimethylacetamideserves as solvent the solution of acrylic polymer and alkali metal saltof an organic sulfonate additionally contains 0.1 to 5.0 percent byweight based upon the total weight of the solution (0.5 to 2.0 percentin a particularly preferred embodiment) of lithium chloride dissolvedtherein. The incorporation of lithium chloride serves the function oflowering and preserving upon standing the viscosity of the solution. Thedesired solution fluidity and mobility for spinning or casting areaccordingly efiiciently maintained even upon the passage of time.

The solution of the acrylic polymer and the alkali metal salt of anorganic sulfonate may be formed by any convenient technique. Forinstance, the acrylic polymer while in particulate form together withthe alkali metal salt of an organic sulfonate may be added to thesolvent with stirring while maintained at about 10 to 100 C. (preferably50 to C.). It is recommended that any heating of the solution in excessof about C. be of limited duration, i.e. no more than a few minutes, sothat no substantial degree of cyclization of pendant nitrile groupswithin the acrylic polymer occurs while dissolved in the solvent.

The solution is preferably filtered such as by passage through a plateand frame press provided with an appropriate filtration medium, prior toforming a fibrous material or film.

The solution containing the acrylic polymer and the alkali metal salt ofan organic sulfonate is preferably converted into a fiber or filmthrough the substantial elimination of the solvent following extrusionthrough a shaped orifice employing conventional solution spinningtechniques (ie. by dry spinning or wet spinning). As is known in theart, dry spinning is commonly conducted by passing the solution throughan opening of predetermined shape into an evaporati-ve atmosphere (e.g.nitrogen) in which much of the solvent is evaporated. Wet spinning iscommonly conducted by passing the solution through an opening ofpredetermined shape into a suitable coagulation bath. Acrylic films mayalso be formed by casting wherein a layer of the solution is placed upona support and the solvent evaporated.

When wet spinning is utilized in the fiber or film forming step of theprocess, a coagulation bath is selected which is capable of preserving aminor quantity of the alkali metal salt of an organic sulfonate withinthe resulting fibrous material or film. More specifically, the bathpreferably exhibits no propensity to leach out and dissolve the alkalimetal salt of an organic sulfonate below the minimum level required topromote the stabilization reaction during the subsequent heat treatmentstep (described hereafter). Such coagulation bath may inherently possessno substantial tendency to dissolve the alkali metal salt of an organicsulfonate. Alternatively, the coagulation bath which is selected mayhave its inherent tendency to dissolve the alkali metal salt of anorganic sulfonate diminished by preliminarily dissolving a substantialquantity of the alkali metal salt of an organic sulfonate or othercompound therein. A preferred wet spinning technique is disclosed incommonly assigned US. Pat. No. 3,657,409, which is herein incorporatedby reference.

The shaped orifice or spinneret utilized during the extr-usion maycontain a single hole through which a single filament is extruded, andpreferably contains a plurality of holes whereby a plurality offilaments may be simultaneously extruded in yarn form. The spinneretpreferably contains holes having a diameter of about 50 to 150 micronswhen producing relatively low denier fibers having an as-spun denier ofabout 8 to 24 denier per filament. Alternatively, acrylic films ofrelatively thin thickness, e.g. about 1 to 10 mils, may be formed, whenthe extrusion orifice is a rectangular slit. Generally stated, thesolution may be formed into an acrylic fibrous material or film having aminor quantity of the stabilization promoting agent incorporated thereinutilizing conventional fiber or film forming techniques with a minorquantity of an alkali metal salt of an organic sulfonate being merelyadded to the polymer dope.

The resulting as-spun fibrous material or film is preferably maintainedin a continuous length configuration throughout the process. At anintermediate point prior to heat treatment the fibrous material mayalternatively be transformed into another fibrous assemblage, e.g. atow, fabric, or yarn of greater total denier.

When the fibrous material is a continuous multifilament yarn, a twistmay be imparted to the same to improve the handling characteristics. Forinstance, a twist of about 0.1 to 5 t.p.i. (turns per inch), andpreferably about 0.3 to 1.0 t.p.i. may be utilized. Also a false twistmay be used instead of or in addition to a real twist. Alternatively,one may select bundles of fibrous material which possess substantiallyno twist.

The fibrous material may be drawn in accordance with conventionaltechniques in order to improve its orientation. For instance, thefibrous material may be drawn by stretching while in contact with a hotshoe at a temperature of about 140 to 160 C. Additional representativedrawing techniques are disclosed in US. Pat. Nos. 2,455,173; 2,948,581;and 3,122,412. It is recommended that fibrous materials prior to theheat treatment (described hereafter) be drawn to a single filamenttenacity of at least about 3 grams per denier. If desired, however, thefibrous material may be more highly oriented, e.g. drawn up to a singlefilament tenacity of about 7.5 to 8 grams per denier, or more.Additionally, the acrylic films optionally may be either uniaxially orbiaxially oriented prior to the heat treatment (described hereafter).

Immediately prior to the heat treatment step the acrylic fibrousmaterial or film commonly contains the alkali metal salt of an organicsulfonate incorporated therein in a. concentration of about 0.2 to 10percent by weight, and preferably in a concentration of about 0.5 to 5percent by Weight.

The acrylic material containing the alkali metal salt of an organicsulfonate incorporated therein is heated at a temperature of about 240to 310 C. until a stabilized fibrous product or film is formed which iscapable of undergoing carbonization, retains its original configurationsubstantially intact and which is non-burning when subjected to anordinary match flame. It is preferred that the acrylic material bepresent in an oxygen-containing atmosphere during the heating, e.g. bepresent in a gaseous atmosphere containing about 20 to 40 percent byweight molecular oxygen. Inert atmospheres such as nitrogen, argon, andhelium may alternatively be provided in the heating zone. In aparticularly preferred embodiment of the process the oxygen-containingatmosphere is air. Preferred temperatures for the oxygen-containingatmosphere range from about 240 to 300 C. (eg. 280 to 300 C.). Ifdesired, the fibrous material or film may be exposed to a temperaturegradient wherein the temperature is progressively increased.

For best results, uniform contact during the stabilization reaction withmolecular oxygen throughout all portions of the alkali metal salt of anorganic sulfonate containing acrylic material is encouraged. Suchuniform reaction conditions can best be accomplished by limiting themass of fibrous material or film at any one location so that heatdissipation from within the interior of the same is not unduly impaired,and free access to molecular oxygen is provided. For instance, theacrylic fibrous material or film may be placed in the heating zone whilewound upon a support to a limited thickness. In a preferred embodimentof the invention, the acrylic fibrous material or film is continuouslypassed in the direction of its length through the heating zone whilesubstantially suspended therein. For instance, a continuous length ofthe acrylic fibrous material or film may be passed through a circulatingoven or the tube of a muifie furnace. The speed of passage through theheating zone will be determined by the size of the heating zone and thedesired residence time.

The period of time required to complete the stabilization reactionwithin the heating zone is generally inversely related to thetemperature of the gaseous atmosphere therein, and is also influenced bythe denier of the acrylic fibrous material or the thickness of the filmundergoing treatment, and the concentration of molecular oxygen (if any)in the atmosphere. Treatment times in the heating zone accordinglycommonly range from about 7 to 180 minutes. For instance, representativeresidence times at specific temperatures are as follows.

Temperatures, C.: Residence time, minutes 240 180 260 65 280 35 310 7Regardlessof the stabilization temperature selected within the range ofabout 240 to 310 C., the presence of the alkali metal salt of an organicsulfonate within the acrylic fibrous material or film results in acontrolled and accelerated stabilization reaction at a given temperaturewhich precludes mass exothermic reactions from taking place.

The stabilized acrylic fibrous materials or films formed in accordancewith the present process are black in appearance, dimensionally stable,flexible, retain essentially the same configuration as the startingmaterial, are nonburning when subjected to an ordinary match flame, whenheated in an oxygen-containing atmosphere commonly have a bound oxygencontent of at least 7 (e.g. 7 to 12) percent by weight as determined bythe Unterzaucher or other suitable analysis, and commonly contain fromabout 50 to 65 percent carbon by weight.

The theory whereby the alkali metal salts of an organic sulfonate serveto accelerate the stabilization reaction is considered complex andincapable of simple explanation. It is believed, however, that thecyclization reaction is catalyzed and caused to proceed at anaccelerated rate in a controlled manner.

When a shaped acrylic article, e.g. an acrylonitrile homopolymer fiberor film, which has not undergone any previous thermal stabilization isheated in air from room temperature (i.e. 25 C.) at a rate of 15C./minute, a weight loss of about 25 percent is observed when atemperature of about 325 to 330 C. is reached. This weight loss isaccompanied by a spontaneous exotherm which is attributed to thecyclization of pendant nitrile groups and a simultaneous chain scissionreaction with the evolution of low molecular weight products, e.g. NHNCN, CH CH CN, etc. Alternatively, if the shaped acrylic article hasincorporated therein 1 to percent of an alkali metal salt of an organicsulfonate, upon undergoing an identical thermal treatment a weight lossof only about 10 percent is observed when heating up to about 325 to 330C. Accordingly, the process of the present invention makes possible alower weight loss during the stabilization reaction, as well asaccelerates the same. The resulting stabilized products if subsequentlyconverted to carbon fibers or films likewise produce a higher eventualcarbon yield.

The stabilized fibrous material resulting from the stabilizationtreatment of the present invention is suitable for use in applicationswhere a fire resistant fibrous material is required. For instance,non-burning fabrics may be formed from the same. As previouslyindicated, the stabilized acrylic fibrous materials are particularlysuited for use as intermediates in the production of carbonized fibrousmaterials. Such amorphous carbon or graphitic carbon fibrous productsmay be incorporated in a hinder or matrix and serve as a reinforcingmedium. The carbon fibers may accordingly serve as a lightweight loadbearing component in high performance composite structures which findparticular utility in the aerospace industry.

The stabilized film resulting from the stabilization treatment issuitable for use in applications Where a fire resistant sheet materialis required. Such stabilized films may also be utilized as intermediatesin the production of carbonized films. Such carbonized films may beutilized in the formation of lightweight high temperature resistantlaminates when incorporated in a matrix material (e.g. an epoxy resin).

The following examples are given as specific illustrations of theinvention. It should be understood, however, that the invention is notlimited to the specific details set forth in the examples.

EXAMPLE I 871 parts by weight polyacrylonitrile homopolymer, 4.36 partsby weight sodium methallyl sulfonate, and 79 parts by weight lithiumchloride are slurried in 3000 parts by weight N,N-dimethylacetamide atroom temperature. The slurry is heated to 100 C. in 65 minutes whilepresent in a closed vessel and held at that temperature for about 29hours. The resulting dope containing the acrylonitrile homopolymer andthe sodium methallyl sulfonate dissolved in N,N-dimethylacetamide ispassed through a conventional filter press while at 100 C. The low shearviscosity (Brookfield) of the resulting spinning solution afterdegassing is found to be 135 poises at 27 C.

The solution while at room temperature (i.e. 25 C.) is fed to a standardcup type spinneret of holes each having a diameter of microns. Thesolution is then passed at a rate of 7.1 cc./min. into a coagulationbath consisting of 66 parts by weight ethylene glycol and 34 parts byweight N,N-dimethylacetamide which is provided at 50 C. The extrusionvelocity is 11.1 meters/ minute, and the velocity as the fiber exitsfrom the coagulation bath is 15 meters/minute thereby accomplishing aslight draw in the coagulation bath.

The resulting fiber is washed with water at 14 C., drawn at a draw ratioof 2:1 while immersed in glycerin provided at 90 C., washed with waterat 14 C., dried, and subsequently drawn at a draw ratio of 5:1 whilepassing over a hot shoe at C. The resulting fiber possesses a singlefilament tenacity of about 3.5 grams per denier, contains about 0.5percent by weight of free sodium methallyl sulfonate incorporatedtherein, and the pendant nitrile groups of the acrylonitrile unitspresent therein are substantially uncyclized.

The fiber is next stabilized on a continuous basis by passage for 12minutes through a circulating heated air atmosphere provided in a tubefurnace having a temperature of 300 C. while axially suspended therein.

The resulting stabilized yarn is capable of undergoing carbonization,shiny black in appearance, flexible, has a textile-like hand, retainsits original fibrous configuration substantially intact, is non-burningwhen subject to an ordinary match flame, retains strength after glowingin a match flame, and has an oxygen content in excess of 8 percent byweight as determined by the Unterzaucher analysis.

In a control run, an identical sample of the acrylonitrile homopolymeryarn is passed throught the tube furnace in an identical manner with theexception that it contains no sodium methallyl sulfonate incorporatedtherein. The control sample exhibited a violet exotherm which wasaccompanied by disintegration.

The resulting stabilized yarn of Example I is carbonized and graphitizedin accordance with the teachings of U.S. Ser. No. 777,275, filed Nov.20, 1968, of Charles M. Clarke (now abandoned), which is hereinincorporated by reference. The graphite yarn exhibits satisfactorytensile properties.

EXAMPLE II Example I is repeated with the exception that the solutioncontains 45 parts by weight of sodium dodecyl benzene sulfonate in placeof the sodium methallyl sulfonate. The resulting fiber contains about 5percent sodium dodecyl benzene sulfonate incorporated therein whichserves to promote the stabilization reaction.

EXAMPLE III Example I is repeated with the exception that the solutioncontains 45 parts by weight of sodium polypropylene sulfonate in placeof the sodium methallyl sulfonate. The resulting fiber contains about 5percent sodium polypropylene sulfonate incorporated therein which servesto promote the stabilization reaction.

EXAMPLE IV Example I is repeated with the exception thatN,N-dimcthylformamide is substituted for the N,N-dimethylacetamidesolvent and the acrylonitrile homopolymer fiber containing sodiummethallyl sulfonate incorporated therein in a concentration of about 0.5percent by weight is formed by extruding the solution while at 140 C.through a spinneret into a dry spinning column. The column containscirculating nitrogen at 180 C. which substantially evaporates theN,N-dimethylformamide. Substantially similar results are achieved uponstabilization.

9 EXAMPLE v Example I is repeated with the exception that the solutionof acrylonitrile homopolymer and sodium methallyl sulfonate is extrudedthrough a rectangular slit having a height of 8 mils into ethyleneglycol to form a film.

Following washing and orientation the resulting film containing about0.5 percent by Weight of free sodium methallyl sulfonate is suspendedfor 15 minutes in a circulating air oven provided at 300 C. wherein itis converted to a stabilized form while retaining its originalconfiguration substantially intact.

The resulting stabilized film is capable of undergoing carbonization,shiny black, flexible, non-burning when subjected to an ordinary matchflame, and contains an oxygen content of about 8 percent by Weight asdetermined by the Unterzaucher analysis.

EXAMPLE VI A thin layer of the solution of acrylonitrile homopolymer andsodium dodecyl benzene sulfonate of Example II is placed upon a flatsupport and the N,N-dimethy1- acetamide solvent evaporated by contactwith circulating hot air provided at 90 C.

Following washing and orientation the film contains about 5 percentsodium dodecyl benzene sulfonate by Weight, and is stabilized asdescribed in Example V to produce substantially similar results.

Although the invention has been described with preferred embodiments, itis to be understood that variations and modifications may be resorted toas will be apparent to those skilled in the art. Such variations andmodifications are to be considered within the purview and scope of theclaims appended hereto.

We claim:

1. An acrylic fibrous material or film consisting essentially of (1) anacrylic polymer selected from the group consisting of an acrylonitrilehomopolymer and acrylonitrile copolymers containing at least about 85mol percent of acrylonitrile units and up to about 15 mol percent of oneor more monovinyl units copolymerized therewith, and (2) about 0.2 topercent by weight of an alkali metal salt of an organic sulfonate, withsaid alkali metal salt of an organic sulfonate being incorporatedtherein in a non-polymerized form and being capable of promoting thethermal stabilization thereof upon heating.

2. An acrylic shaped article according to claim 1 wherein said acrylicmaterial is a fibrous material.

3. An acrylic shaped article according to claim 1 wherein said acrylicmaterial is a film.

4. An acrylic fibrous material or film according to claim 1 wherein saidalkali metal salt of an organic sulfonate which is capable of promotingthe thermal stabiliza tion of said acrylic polymer is sodium methallylsulfonate.

5. An acrylic fibrous material or film according to claim 1 wherein saidalkali metal salt of an organic sul- 10 fonate is present in aconcentration of about 0.5 to 5 percent by weight.

6. An acrylic fibrous material or film consisting essentially of (1) anacrylic polymer selected from the group consisting of an acrylonitrilehomopolymer and acrylonitrile copolymers containing at least about molpercent of acrylonitrile units and up to about 15 mol percent of one ormore monovinyl units copolymerized therewith, and (2) about 0.2 to 10percent by weight of an alkali metal salt of an alkylaryl sulfonate,with said alkali metal salt of an alkylaryl sulfonate being incorporatedtherein in a non-polymerized form and being capable of promoting thethermal stabilization thereof upon heating.

7. An acrylic shaped article according to claim 6 wherein said acrylicmaterial is a fibrous material.

8. An acrylic shaped article according to claim 6 wherein said acrylicmaterial is a film.

9. An acrylic fibrous material or film according to claim 6 wherein saidalkali metal salt of an organic sulfonate is present in a concentrationof about 0.5 to 5 percent by weight.

10. An acrylic fibrous material or film according to claim 6 whereinsaid alkali metal salt of an alkylaryl sulfonate contains at least onealkyl group having up to about 30 carbon atoms.

11. An acrylic fibrous material or film according to claim 10 whereinsaid alkali metal salt of an alkylaryl sulfonate contains at least onealkyl group having 10 to 20 carbon atoms.

12. An acrylic fibrous material or film according to claim 11 whereinsaid alkali metal salt of an alkylaryl sulfonate which is capable ofpromoting the thermal stabilization of said acrylic polymer is sodiumdodecylbenzene sulfonate.

References Cited UNITED STATES PATENTS 3,679,354 7/1972 Hildebrand eta1. 8-177 R 3,476,698 11/1969 Osterrieth et a1. 26030.8 R 2,279,771 4/1942 Austin 26030.-8 R 3,528,947 9/ 1970 Lappin et a1 26030.8 R3,583,941 6/1971 Trapasso et a1. 260-30.8 R 3,630,986 12/1971 Mison etal 260-308 R 3,622,658 11/1971 Nakagawa 8-168 3,627,473 12/ 1971Eltonhead 8177 R 3,663,161 5/1972 Litzler et al 8-177 R OTHER REFERENCESThe Condensed Chemical Dictionary, 7th ed., Reinhold PublishingCorporation, New York, N.Y., 1966, p. 15.

DONALD E. CZAJA, Primary Examiner R. W. GRIFFIN, Assistant Examiner U.S.Cl. X.R.

